A cheap hobby. Why collect Hot Wheel cars, coins, stamps?
Even thought the Techs continued through to the 70s, the "TTO" (twist to open) razors started to appear in the late 40s, and throughout the 50s. You probably remember your grandfathers using these, twist the bottom and the butterfly doors would open. They were called "Super Speeds" and evolved into two different designs. They started with the straight TTO knob.
And then evolved into the flare TTO knob. 90% had the nickel knob, but a few came with red tip (more aggressive) and a blue tip (milder).
What I've been showing are the basic highly produced "working man's" razors, but Gillette did make specialty through the years. Aristocrats, Senators, Executives, Sheratons, Milords, etc. Here's a 1953 President I found that looked like it had been in a shower for 60 years, just caked with soap scum and mildew. It turned out to be rhodium!